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Parabolic Trough Collector

A Parabolic Trough Collector is widely used among the various solar thermal energy technologies used for generating solar thermal electricity. In order to obtain elevated temperature and better efficiency a high quality solar collector system is required.

Parabolic Trough Collector is a type of Parabolic Solar Collector like Compound Parabolic Collectors, Parabolic Dish Reflectors etc. A typical Parabolic Trough is made up of sheets of reflective material like highly polished mirrors bent into a parabolic shape.

Image by Tom Raftery

Parabolic Troughs differ from each other in terms of structural material, reflective material and even by concept of receivers. The design of the collector depends upon the temperature application as factors such as receiver losses, surface error, tracking error become very much significant during the design process.

They are built in modules and are arranged together to form a system using ground supports with pedestals at either ends.

A Black metal tube runs along the focal line of the trough collector. Many times this tube is coated by a glass tube from the outside. This tube uses vacuum in order to stop loss of heat by radiation. The size of the tube and thus the concentration ratio depends upon the size of the reflected sun image and the manufacturing tolerances for the parabolic trough.

But how does this help in Electricity Generation?

When the highly reflective parabolic trough is exposed to the incident solar radiation, it is converted into usable format i.e. heat.

Incident light rays after striking the surface of the parabolic reflector are concentrated at the focus of the trough collector. As the parabolic trough collector has lengths ranging from 25 metres to 150 metres. All we get is a focal line along the length of the trough which strikes the receiver pipe. Circulating fluid in the receiver pipe gets heated thereby converting solar radiation into usable heat.

The circulating fluid reaches a temperature around 400° C. The circulating heat transfer fluid is then used to heat steam or generate steam which drives a conventional steam turbine to produce electricity from the generator. The efficiency of the systems utilizing parabolic troughs is about 15% to 18% which is very much similar to photovoltaic systems.

The biggest installation in the world is SEGS in California with a mammoth generating capacity of 354MWe. A few electricity generating plants in Europe on the MWe scale also use parabolic trough collectors.

World Wide Scenario

More and more electricity generation plants all over the world are being setup using solar energy. Developing Countries too have taken initiatives in this direction especially India & China have shown keen interest and growth in this area.

The Government of India recently launched its National Solar Mission to promote the use & implementation of Solar Thermal as well as Solar PV projects.

Solar Parabolic trough collector is a mature technology and is a key contributor for generating clean and affordable electricity for all of us, all over the world and for years to come.